This invention relates to a gas mixture feed system of an internal combustion engine, and more particularly to a gas mixture feed system provided therein with an exhaust gas recirculating device suitable for use in decreasing the quantities of nitrogen oxide and the like.
Heretofore there has been used an exhaust gas recirculating device adapted to introduce part of exhaust gas to an intake pipe for decreasing the quantity of nitrogen oxide contained in the exhaust gas of the internal combustion engine. It is well known that, if the ratio between the quantity of recirculated exhaust gas and the quantity of air intake is termed as an exhaust gas recirculation rate, then the quantity of nitrogen oxide discharged is decreased with the increase of the exhaust gas recirculation rate. However, if the exhaust gas recirculation rate is increased, then combustion becomes unstable and the quantities of carbon monoxide and hydrocarbon are increased. Consequently, in order to decrease the quantities of nitrogen oxide without causing carbon monoxide and hydrocarbon to be increased in quantities, it is necessary to control the exhaust gas recirculation rate within a narrow range as shown by hatching in FIG. 1.
The conventional exhaust gas recirculating device for the internal combustion engine is of such an arrangement that part of exhaust gas is recirculated to the portion of intake pipe, which is disposed downstream of the throttle valve of the carburetor. For this, the air-fuel mixture and the exhaust gas recirculated are mixed not uniformly in the intake pipe, considerable differences are found between the exhaust gas recirculation rates of the respective cylinders in the case of a multi-cylinder engine as shown in FIG. 2, and difficulties have been felt in accurately controlling the exhaust gas recirculation rates. Further, since the negative pressure downstream of the throttle valve varies to a considerable extent in accordance with the operating conditions of the engine, the quantity of exhaust gas recirculated also varies to a considerable extent, and the exhaust gas recirculation rate varies on the whole. There has been a practice to provide a control valve in the exhaust gas recirculating passageway in order to prevent the variation in said exhaust gas recirculation rate. Said conventional control valve is of the type having a diaphragm to be driven in accordance with the Venturi negative pressure in the carburetor. With said control valve, there is such a shortcoming that accuracy in controlling of the exhaust gas recirculation rate is decreased at the time of operating conditions of low Venturi negative pressure, i.e., at low speed and low load.